Title:
Froth skimming and crowding device for flotation machines
United States Patent 2369401
Abstract:
This invention relates to an improvement in mechanical froth flotation machines. Froth flotation machines present a considerable problem in froth overflow, particularly when highly mineralized froths are produced, or where It is attempted to float relatively coarse particles. The ability of...


Inventors:
Norman, Morash
Application Number:
US50455043A
Publication Date:
02/13/1945
Filing Date:
10/01/1943
Assignee:
AMERICAN CYANAMID CO
Primary Class:
International Classes:
B03D1/16
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Description:

This invention relates to an improvement in mechanical froth flotation machines.

Froth flotation machines present a considerable problem in froth overflow, particularly when highly mineralized froths are produced, or where It is attempted to float relatively coarse particles. The ability of the bubbles of the froth to sustain heavy weights of minerals is limited because the bubbles tend to break or drop their mineral load unless they are promptly removed from the machine. For this reason various froth skimming devices have been used. In rectangular machines it is common to have mechanically driven paddles along the two froth overflow lips which slowly turn and skim off the froth. It has also been proposed a few years ago to apply mechanically driven rotary skimmers to froth flotation machines of the round type. Both of these devices are of considerable help in the rapid removal of mineralized froth. However, they are open to a number of disadvantages. For one thing, they require a separate mechanical drive and in the case of rectangular machines usually two drives with resulting additional power consumption and complication. Skimming devices operating close to the froth overflow lip also do not skim efficiently the froth located more nearly in the center of the machine and as the central vortex is the point where there is maximum agitation it is also the point where bubbles are most readily broken and the necessity of rapid removal is at a maximum. An even more serious disadvantage of the conventional types of froth skimmers lies in the fact that they are driven at a constant predetermined speed. As a result, if the skimming speed is adjusted for certain conditions of froth, changes in these conditions will find the skimming device operating at a speed which is not the optimum.

Ideally a froth flotation machine should release its froth over a relatively narrow area of surface immediately adjacent to froth overflow lips and the skimming device should remove the froth from this narrow zone promptly and at a speed which is adjusted for the particular conditions. Even the most efficient skimming devices hitherto used fall far short of this ideal.

As has been pointed out above, the skimming is at constant speed and difficulties are encountered in removing the froth from the central portions of the machine without excessive loss of its mineral particles. The present invention is an improved device which closely approaches ideal conditions and permits material improvement in the operation of mechanical froth flotation machines of the circular or more generally non-elongated type.

According to the present invention a freely rotatable cone is centrally mounted in the cell with its apex extending down into the central vortex, the tip of the cone being cut off to permit the drive shaft for the agitating means to pass through in the case of machines driven from the top-which is the more common type. The conical surface of the device of the present invention extends to a point fairly near the overflow lip so'that the surface of liquid in the cell is in the form of a narrow annulus. Fins are attached to the conical device so that the rotary motion of the pulp in the cell due to the rotary ,agitating means tends to turn the device which is provided with skimming blades at its periphery.

In operation, therefore, the device spins at a speed which is governed by the operation of the cell, the froth is crowded into a narrow annulus and is immediately skimmed into the launder.

The device of the present invention performs two functions simultaneously, namely the crowding of the froth into a narrow surface of disengagement and immediately skimming of the froth which rises to the surface. At the same time the device does not require additional power or rather the power requirements are negligible and it automatically adjusts itself to operating conditions. If the agitating means is speeded up resulting in a more rapid vortex the skimmer and froth crowding device of the present invention spins faster. The same is true where there is a very violent froth disengagement which increases the volume of rising material and hence the speed with which the pulp swirls in the cell.

Over a wide range, therefore, optimum skimming rate can be maintained by a suitable design of the driving fins and skimming blades of the present invention.

It is an. advantage of the present invention that the device is simple, extremely cheap to manufacture, and requires practically no maintenance. It also does not add to the compli46 cation of flotation machine drives.

The operation of the device of the present invention is most simple in a circular flotation machine where the round overflow lip is concentric with the rotating agitating means, and it is precisely this type of machine which is most difficult to skim satisfactorily by the conventional skimming devices involving rotating paddles. However, the invention is not limited to a machine which is exactly circular. On the contrary it is 6B possible to use the device for a square machine or even in a rectangular machine, provided it is not too elongated. Thus in a square machine or a rectangular machine in which the pairs of sides do not differ greatly in length a somewhat longer skimmer blade will operate satisfactorily. The device of the present invention is not well suited for very long narrow machines. In the case of rectangular machines the overflow lip may extend only on two sides. In such cases the length of the skimmer blades is chosen so that they will skim froth satisfactorily over the two sides. In the claims the term "non-elongated" will be used to describe circular machines, square machines, and machines of substantially rectangular shape in which the difference in length of the pairs of sides is not great. It should be understood that this term is intended to have no other meaning.

The invention will be described in greater detail in connection with a circular froth flotation machine of the Fagergren type, but it is an advantage of the present invention that it is not limited to this machine but is useable in any mechanical circular machine in which rotary agitating means are employed.

The description of the details of the machine is in connection with the drawings in which: Fig. 1 is a vertical elevation, partly in section; Fig. 2 is a horizontal section along the lines 2-2; and Fig. 3 is a detailed elevation of the skimming and crowding device.

A typical round Fagergren flotation machine is shown in the drawings having a flotation chamber 1, provided with a standard Fagergren squirrel cage rotor and stator 2, pulp inlet 4. and tailings outlet 5, and a circular froth launder 3.

The rotor is driven by the shaft 6 by means of the pulley 7 from a source of power not shown.

The shaft is journaled in a stationary hollow shaft 8 through which air is introduced through the valved inlet in the customary manner. On this stationary shaft there is mounted the frusto conical device 9 of the present invention, which is provided with a flange 16 forming a housing for a bearing 10 on a collar 15 fastened to the shaft 8. The conical device is attached to the bearing by the flat spokes II and is provided with two skimming blades 12 and a pair of deep fins 13 and shallow fins 14 extending into the pulp in the cell.

When the flotation machine is operating the tangential discharge from the rotor through the stator causes the pulp in the cell to swirl forming a vortex. The swirling of the pulp spins the skimming device by means of the fins 13 and 14.

Froth is crowded by the conical surface so that it reaches the surface of the cell in a narrow annulus between the outer periphery of the crowding and skimming device and the froth overflow lip. The skimming blades 12 remove the froth promptly from this narrow zone before any considerable loss of mineral particles can take place.

It should be noted that since the drive of the skimming device is not mechanical but is merely dependent on the vortex in the flotation cell anything which increases the rotation of this vortex will speed up the rotation of the skimming and crowding device. As the speed of the agitator is increased so will the speed of the vortex and more rapid skimming will result which is needed in order to take care of the larger amount of froth. Similarly where the frothing is very heavy the spinning in the cell will increase and correspondingly more rapid skimming will take place. Within wide ranges, therefore, the device of the present invention will automatically adjust itself to changes in operating conditions of the cell requiring, therefore, a minimum of adjustment during operation.

The device of the present invention is applicable to round froth flotation machines of various types used with various ores and reagents. It is particularly important in operations where skimming is a serious problem, for example certain non-metallic operations such as phosphate flotation, the clarification of lubricating coolants by froth flotation means, and the like. While the device of the present invention will adjust itself to changes in operating conditions, it is desirable to design and dimension the device for best results with a particular type of froth flotation operation- However, over a wide range no material changes in design are necessary and, therefore, devices of the present invention may be used interchangeably in a number of operations.

The conical portion of the device of the present invention is shown as hollow. This is the most satisfactory mechanical design in most cases. However, it is not essential and a solid cone may be used in some cases but its extra weight usually renders it undesirable.

I claim: 1. In a non-elongated mechanical froth flotation machine provided with a rotary agitating means driven by a verticle shaft rising above the machine, the improvement which comprises an inverted conical body rotatably mounted concentric with said shaft and leaving a narrow space between its-periphery and the froth overflow lips of the machine, fins attached to the conical body and extending out radially into the pulp to cause the conical body to rotate with swirling of the pulp in the machine, and skimming blades attached to the periphery of the conical body positioned to skim froth over the overflow lips into the froth launder of the machine.

2. In a round froth flotation machine of the mechanical type provided with a central rotary 56 agitator driven by a vertical shaft rising above the machine, the improvement which comprises an inverted conical body rotatably mounted concentric with said shaft and leaving an annular space between its periphery and the froth overflow lip of the machine, fins attached to the conical body and extending out radially to cause it to rotate with swirling of the pulp in the machine, and skimming blades attached to the periphery of the conical body positioned to skim froth over the 9verflow lip into the froth launder of the machine.

NORMAN MORASH.